In the exploration, drilling, and production of hydrocarbons, it becomes necessary to drill directional and horizontal wells. As those of ordinary skill in the art appreciate, directional and horizontal wells can increase the production rates of reservoirs. Hence, the industry has seen a significant increase in the number of directional and horizontal wells drilled. Additionally, as the search for hydrocarbons continues, operators have increasingly been targeting thin beds and/or seams with high to very low permeability. The industry has also been targeting conventional and unconventional hydrocarbon reservoirs such as tight sands, shales, carbonates, lime stone, chert, salt domes, ash, anhydrate, and coal.
Traditionally, these thin bed reservoirs, coal seams, shales and sands may range from less than five feet to greater than twenty feet. In the drilling of these thin zones, operators attempt to steer the drill bit within these zones. As those of ordinary skill in the art will recognize, keeping the wellbore within the zone is highly desirable for several reasons including, but not limited to, maintaining greater drilling rates to reduce the number of drilling days, maximizing production rates once completed, limiting water production, preventing wellbore stability problems, exposing more productive zones, keeping the wellbore clean, reducing torque and drag, smoother production casing runs, etc.
Various prior art techniques have been introduced. However, all these techniques suffer from several problems. For instance, in the oil and gas industry, it has always been an accepted technique to gather surface and subsurface information and then map or plot the information to give a better understanding of what is actually happening below the earth's surface. Some of the most common mapping techniques used today includes elevation contour maps, formation contour maps, sub-sea contour maps, seismic maps, synthetic maps, and formation thickness (isopac) maps.
Some or most of these can be presented together on one map or separate maps. For the most part, the information that is gathered to produce these maps are from electric logging and real time measurement while drilling and logging devices (gamma ray, resistivity, density neutron, sonic or acoustic, surface and subsurface seismic, or any available electric log). This type of data is generally gathered during, or after a well is drilled. Additionally, measurement while drilling and logging while drilling techniques allow the driller, real time access while drilling to subterranean data such as gamma ray, resistivity, density neutron, and sonic or acoustic and subsurface seismic. This type of data is generally gathered during the drilling of a well.
These logging techniques have been available and used by the industry for many years. However, there is a need for a technique that will utilize historical well data and real time surface and downhole data to steer the bit through a zone of interest. There is a need for a method that will produce, in real time during drilling, an instantaneous dip for a very thin target zone. There is also a need for a process that will utilize the instantaneous dip, at user specified intervals, to produce a calculated target window (top and bottom) and extrapolate this window ahead of the projected well path so an operator can keep the drill bit within the target zone identified by the calculated dip and associated calculated target window. There is a further need for a process that can identify and modify a target zone without the need to stop drilling.
In the normal course of drilling, at user specified intervals, surveys are periodically performed. As those of ordinary skill in the art will appreciate, in order to guide a wellbore to a desired target, the position and direction of the wellbore at any particular depth must be known. Since the early days of drilling, various tools have been developed to measure the inclination, azimuth, and vertical depth of the wellbore.
In order to calculate the three-dimensional path of the wellbore, it is necessary to take measurements, at user specified intervals, along the wellbore at known depths of the inclination angle (angle from vertical) and azimuth angle (direction normally relative to true north). These measurements are called surveys and are typically conducted when drilling has temporarily ceased but can also be produced while drilling the well.
Prior art survey tools include those such as but not limited to: steering tools, tools associated with measurement while drilling (MWD), electro-magnetic measurement while drilling (EM-MWD), and magnetic single shot (MSS). One such method, after drilling a hole section of a well, a wireline survey is run inside the drill pipe before pulling out with the drill bit, or by running a wireline survey inside the steel casing once it is cemented in place. During drilling, many government regulations require the running of a wireline survey or getting an MWD survey, or EM-MWD survey, in some cases every 200 feet for horizontal or deviated wells and every 500 feet for vertical wells.
In today's environment of drilling and steering in ultra-thin target zones, knowing the true stratigraphic position and direction of the bit within the true stratigraphic formation is critical. Operators need to know the accurate position of the bit and bit projection path. In the event of an actual deviation from a planned stratigraphic wellbore projection path, time is critical in order to correct the bit direction back to the planned true stratigraphic path to prevent the bit from drilling into nonproductive zones.